Light emitting diode thermally enhanced cavity package and method of manufacture

ABSTRACT

Several embodiments of light emitting diode packaging configurations including a substrate with a cavity are disclosed herein. In one embodiment, a cavity is formed on a substrate to contain an LED and phosphor layer. The substrate has a channel separating the substrate into a first portion containing the cavity and a second portion. A filler of encapsulant material or other electrically insulating material is molded in the channel. The first portion can serve as a cathode for the LED and the second portion can serve as the anode.

TECHNICAL FIELD

The present disclosure is related to solid state lighting (SSL) devicesand associated methods of operation and manufacture. In particular, thepresent disclosure is related to light emitting diodes (LEDs) andassociated methods of packaging.

BACKGROUND

Mobile phones, personal digital assistants (PDAs), digital cameras, MP3players, and other portable electronic devices utilize SSL devices(e.g., white light LEDs) for background illumination. However, truewhite light LEDs are not available because LEDs typically only emitlight at one particular wavelength. For human eyes to perceive the colorwhite, a mixture of wavelengths is needed.

One conventional technique for emulating white light with LEDs includesdepositing a converter material (e.g., a phosphor) on a light emittingmaterial. For example, as shown in FIG. 1A, a conventional LED device 10includes a support 2 carrying an LED die 4 and a converter material 6deposited on the LED die 4. The LED die 4 can include one or more lightemitting components. For example, as shown in FIG. 1B, the LED die 4 caninclude a silicon substrate 12, N-type gallium nitride (GaN) material14, an indium gallium nitride (InGaN) material 16 (and/or GaN multiplequantum wells), and a P-type GaN material 18 on one another in series.The LED die 4 can also include a first contact 20 on the P-type GaNmaterial 18 and a second contact 22 on the N-type GaN material 14.Referring to both FIGS. 1A and 1B, in operation, the InGaN material 16of the LED die 4 emits a blue light that stimulates the convertermaterial 6 to emit a light (e.g., a yellow light) at a desiredfrequency. The combination of the blue and yellow emissions appearswhite to human eyes if matched appropriately.

One operational difficulty of the LED device 10 is that the LED die 4produces a significant amount of heat. The generated heat raises thetemperature of the converter material 6, and thus causes the convertermaterial 6 to emit light at a different frequency than the desiredfrequency (a phenomenon commonly referred to as “thermal quenching”). Asa result, the combined emissions would appear off-white and may reducethe color fidelity of electronic devices. Accordingly, severalimprovements in managing the thermal load in LED packages may bedesirable.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a schematic cross-sectional diagram of an LED device inaccordance with the prior art.

FIG. 1B is a schematic cross-sectional diagram of an LED die inaccordance with the prior art.

FIG. 2 is a partially schematic cross-sectional view of amicroelectronic LED package in accordance with the new technology.

FIG. 3A is a partially schematic cross-sectional view of a manufacturingprocess for a microelectronic LED package in accordance with the newtechnology.

FIG. 3B is a partially schematic cross-sectional view of a manufacturingprocess for a microelectronic LED package in accordance with the newtechnology.

FIG. 3C is a partially schematic cross-sectional view of a manufacturingprocess for a microelectronic LED package in accordance with the newtechnology.

FIG. 4A is a partially schematic top view of a microelectronic device inaccordance with the new technology.

FIG. 4B is a partially schematic top view of a microelectronic device inaccordance with the new technology.

DETAILED DESCRIPTION

Specific details of several embodiments of the new technology aredescribed below with reference to LEDs and light converter materialsincluding phosphor materials, and associated methods of manufacturingLED assemblies. The term “phosphor” generally refers to a material thatemits light when irradiated by energized particles (e.g., electronsand/or photons). A person skilled in the relevant art will understandthat the new technology may have additional embodiments and that the newtechnology may be practiced without several of the details of theembodiments described below with references to FIGS. 2-4B.

FIG. 2 illustrates an LED package 100 in accordance with severalembodiments of the technology. The package 100 includes a conductivesubstrate 110 with a cavity 120, an LED 130 in the cavity 120, and aconverter material 140 configured to be irradiated by the LED 130. Thecavity 120 can be depression, such as a “blind cavity,” that extends toan intermediate depth within the substrate 110 without passingcompletely through the substrate 110. The package 100 can furtherinclude an electrostatic dissipation (ESD) chip 150 and a reflectivematerial 180 lining the cavity 120. The package 100 can also contain aafiller 160 that separates a medial, first portion 115 of the conductivesubstrate 110 from a lateral, second portion 116 of the substrate 110.For example, filler 160 can be a dielectric spacer between the firstportion 115 and the second portion 116 that electrically isolates thefirst portion 115 from the second portion 116. In some embodiments, thepackage 100 also includes a lens 170 over the components in the cavity120. The package 100 can include one or more LEDs 130 in a single cavity120. In some embodiments, the cavity 120 is deeper than the thickness ofthe LED 130 such that the LED fits within the cavity without protrudingabove the surface of the substrate 110.

The conductive substrate 110 can be copper (Cu) or another suitablematerial that has a high thermal and electrical conductivity, such asaluminum (Al), tungsten (W), stainless steel, and/or suitable substancesor alloys. The conductive substrate 110 can also provide mechanicalsupport and rigidity for the package 100. The substrate 110 canaccordingly be a heat sink with a high thermal conductivity to transferheat from the LED 130 and/or the converter material 140.

The package 100 can include a single LED 130 or a plurality of LEDsarranged in an array. The LED 130 can be configured to emit light in thevisible spectrum (e.g., from about 565 nm to about 660 nm), in theinfrared spectrum (e.g., from about 680 nm to about 970 nm), in the nearinfrared spectrum (e.g., from about 1050 nm to about 1550 nm), and/or inother suitable spectra. In some embodiments, the LED 130 is madegenerally similar to the LED die 4 shown in FIG. 1B but instead of thesilicon substrate 12, the LED 130 can have a metallized contact surfaceat the base of the LED 130 made of copper (Cu), aluminum (Al), tungsten(W), stainless steel, and/or other suitable metal and/or metal alloys,or other electrically conductive materials such as silicon carbide(SiC). The contact surface can be a first lead 111 for the LED 130. Inother embodiments, the N-type GaN material 14 serves as the first lead111.

The LED 130 can be surface mounted to the first portion 115 of thesubstrate 110 in the cavity 120 through the first lead 111. The LED 130can have a second lead 117 spaced apart from the first lead 111 andconnected to the second portion 116 of the substrate 110, for example,through a wirebond 195. The first lead 111 in series with the firstportion 115 can be a cathodic lead, and the second lead 117 in serieswith the second portion 116 can be an anodic lead, or vice-versa.Surface mounting the first lead 111 to the first portion 115 largelyeliminates the need for expensive, time-consuming processes required foraligning and connecting very small electrical terminals (e.g.,bond-pads) between conventional LEDs and substrates. For example, thepositional tolerance of a pair of contacts is related, at least in part,to the size of the contacts in the pair. Aligning two, small contactsrequires accurate positioning, while aligning a small contact on alarger surface does not require the same precision. In an embodiment,the first lead 111 comprises the entire contact surface of the LED 130to provide a large contact surface with high positional tolerance.Because the first portion 115 is electrically isolated from the secondportion 116 by the filler 160, a circuit is formed between the firstportion 115, the LED 130, and the second portion 116.

To achieve certain colors of light from the LED 130, a convertermaterial 140 can be used to alter or compliment the color of light thatleaves the LED 130. The converter material 140 can be placed in thecavity 120 over the LED 130 such that light from the LED 130 irradiatesthe phosphor in the converter material 140; the irradiated phosphor thenemits light of a certain quality. Alternatively, the converter material140 can be spaced apart from the LED 130 or in any other location thatis irradiated by the LED 130. The lens 170, for example, can be infusedwith the converter material 140 in a single structure. For example, inone embodiment, the converter material 140 can include a phosphorcontaining cerium(III)-doped yttrium aluminum garnet (YAG) at aparticular concentration for emitting a range of colors from green toyellow and to red under photoluminescence. In other embodiments, theconverter material 140 can include neodymium-doped YAG,neodymium-chromium double-doped YAG, erbium-doped YAG, ytterbium-dopedYAG, neodymium-cerium double-doped YAG, holmium-chromium-thuliumtriple-doped YAG, thulium-doped YAG, chromium(IV)-doped YAG,dysprosium-doped YAG, samarium-doped YAG, terbium-doped YAG, and/orother suitable phosphor compositions. The lens 170 can simply transmitthe light from the LED 130 and converter material 140, or it can furtherfocus or otherwise alter characteristics of the light.

The ESD chip 150 can prevent, mitigate, or dissipate static electricityin the LED package 100. The ESD chip 150 can be positioned in the cavity120 or in any other convenient location.

The reflective material 180 can comprise silver, gold, or anothermaterial with generally high reflectivity and thermal conductivity. Thereflective material 180 can line the cavity 120 to reflect lightproduced by the LED 130 through the converter material 140. Thereflected light accordingly increases the output of the LED package 100rather than being absorbed as heat. The reflective material 180 can bechosen based on its reflective qualities and for the color of light eachmaterial reflects. For example, when the surface of the substrate 110 iscopper, the reflected light will have some copper colored components. Asilver reflective material 180, however, also reflects light butgenerally without coloring the light. When a colored light is desired,the reflective material 180 can be gold or copper or another reflective,colored surface.

FIGS. 3A-3C illustrate processes for manufacturing packaged LEDs inaccordance with several embodiments of the present technology. FIG. 3Adepicts a substrate 210 that can begin as a single sheet of materialsuch as copper (Cu), aluminum (Al), tungsten (W), or another suitablematerial. Preferably, the substrate 210 is made of an electricallyand/or thermally conductive material as described above. A cavity 220can be formed in the substrate 210 by an etching process (e.g., wetetch) or another suitable process. The cavity 220 can be a blind cavityextending into the substrate 210 leaving a bottom surface 222 and asloped perimeter region 224 that can be rounded, angled, or vertical.The etch process can be controlled using a mask 228 covering portions ofthe substrate 210 that are not to be etched.

The structure shown in FIGS. 3A-3B can be made with separate top-sideand bottom-side processes. For example, the cavity 220 and at least aportion of the channel 226 can be formed in the substrate 210 by a firstetch process that removes material from a top-side 221. A second etchprocess can be performed to remove material from a bottom-side 223 ofthe substrate 210 at a location aligned with the location of the firstetch process to complete the channel 226. The etch process can be a wetetch or another suitable process. In other embodiments, the cavity 220and channels 226 can be created using separate and/or differentprocesses, such as molding, pressing, grinding, and/or cutting. Theprocesses of making the channels 226 can be used to separate a solidsubstrate 210 into a first portion 232 and a second portion 234.

FIG. 3B illustrates a manufacturing process according to furtherembodiments of the present technology in which a reflective material 236is formed to line the cavity 222 and a filler 230 is molded in thechannels 226. The reflective material 236 can be plated or formed byvapor deposition or by another, suitable method. The filler 230 can beany type of electrically insulating, moldable material to electricallyisolate the first portion 232 of the substrate 210 from the secondportion 234 and bond the first portion 232 and the second portion 234together. The substrate 210 and the filler 230 form a compositestructure of conductive and non-conductive materials. Additional holesand moldings can be formed into the substrate 210 depending on designconsiderations and to accommodate a host device.

FIG. 3C shows a subsequent portion of a manufacturing process accordingto several embodiments of the present technology in which an LED 240 isplaced in the cavity 220 and electrically connected with the firstportion 232 of the substrate 210. An ESD component 242 can also beplaced in the cavity 220 or in another suitable location to mitigatedamage from static electricity, similar to components explained abovewith respect to LED 130. As explained above, the base of the LED 240 canbe electrically conductive or have a conductive contact thatelectrically couples the LED 240 to the first portion 232 of thesubstrate 210. The backside of the LED 240 can therefore besurface-mounted to the first portion 232 using a solder paste, copperbonding, or other suitable technique. The LED 240 and the ESD component242 can also be connected to the second portion 234 through, forexample, wirebonds 244 or other electrical connection means. Because theexposed surface of the substrate 210 in the cavity 220 is generallyconductive, the positional tolerance for the LED 240 is relatively highand aligning the LED 240 in the cavity 220 is simple and inexpensive.Also, the conductive nature of the substrate 210 helps to dissipate heatproduced by the LED 240.

A converter material 250, such as a phosphor material, can be formed inthe cavity 220 or above the cavity 220. The converter material 250 caninclude a carrier with phosphor particles on and/or embedded in thecarrier. The carrier, for example, can be a thermo-forming resin,silicone, or other suitably transparent material. The cavity 220provides a convenient recess, or depression into which the phosphormaterial can be deposited in a single, easy process without having toform a separate dam on the surface of the substrate 210. Conventionalphosphor structures that are built on a flat surface with no cavitygenerally require a first deposition process to build a dam to hold thephosphor in place, and a second process to fill the dam with thephosphor material. The cavity 220 simplifies and speeds the process byeliminating the need to construct a separate dam. The converter material250 generally fills the cavity 220 and covers the LED 240. In otherembodiments, the converter material 250 may not completely cover the LED240. The converter material 250 can contain any type of phosphor for usewith any type of LED 240 to achieve a desired light characteristic. Alens 252 can be constructed over the LED 240 to further focus or alterthe light from the LED 240. The processes of FIGS. 3A-C produce apackaged LED unit 300.

FIG. 4A is a partially schematic top view of a strip 400 having aplurality of LED units 300 according to the present technology. Manyfeatures of the individual LED units 300 are substantially analogous tofeatures described above with reference to FIGS. 2 and 3A-3C, and can bemade using similar manufacturing techniques. Like reference numbersaccordingly correspond to like elements in FIGS. 2-4A. The strip 400includes the substrate 210, such as a copper substrate, a depression 220for each LED unit 300, and the channel 226 defined by an elongatedtrench near the depression 220. The channel 226 can be filled with amolded filler 230 other suitable electrical insulator. Each LED unit 300has at least one LED 240 and an ESD chip 242 placed in the depression220. The substrate 210 can be cut along lines 410 to separate theindividual LED units 300 from each other, or the substrate 210 canremain intact such that a single device can have multiple individuallypackaged LED units 300. The structures and processes described here canbe applied in batch to many, similar packages in the strip or wafer.

FIG. 4B illustrates an alternative embodiment of the LED package 200 inaccordance with the present technology. Features of the package 200 aregenerally similar to features of FIG. 4A. The package 200 can have asubstrate 210 with a depression 220 that contains multiple LEDs 240 inthe depression 220. Any suitable number of LEDs 240 can be included inthe depression 220. The LEDs 240 may have different characteristics andmay emit light of different frequencies, and the converter material andlens (not shown) can be adjusted as necessary to accommodate themultiple LEDs 240, including using multiple types of convertermaterials. Alternatively, the LEDs 240 can be similarly configured. Thedepression 220 for embodiments including plural LEDs 240 can be largerthan the depression 220 in other embodiments. In other embodiments, thedepression 220 can be of a uniform size large enough to accommodate agiven number of LEDs 240 (e.g., four or five). The uniform size allowsthe package 200 to include up to the given number of LEDs 240 withoutrequiring a different substrate 210 or reconfiguring any process steps.

From the foregoing, it will be appreciated that specific embodiments ofthe invention have been described herein for purposes of illustration,but well-known structures and functions have not been shown or describedin detail to avoid unnecessarily obscuring the description of theembodiments of the invention. Where the context permits, singular orplural terms may also include the plural or singular term, respectively.Unless the word “or” is associated with an express clause indicatingthat the word should be limited to mean only a single item exclusivefrom the other items in reference to a list of two or more items, thenthe use of “or” in such a list shall be interpreted as including (a) anysingle item in the list, (b) all of the items in the list, or (c) anycombination of the items in the list.

Also, it will be appreciated that specific embodiments described aboveare for purposes of illustration and that various modifications may bemade without deviating from the invention. Aspects of the disclosuredescribed in the context of particular embodiments may be combined oreliminated in other embodiments. Further, while advantages associatedwith certain embodiments of the disclosure may have been described inthe context of those embodiments, other embodiments may also exhibitsuch advantages, but not all embodiments need necessarily exhibit suchadvantages to fall within the scope of the disclosure. Accordingly, thepresent invention is not limited to the embodiments described above,which were provided for ease of understanding; rather, the inventionincludes any and all other embodiments defined by the claims.

1. A method for forming a packaged light emitting diode (LED), themethod comprising: forming a cavity in a first portion of a substrate;separating the first portion of the substrate from the second portion ofthe substrate; forming a filler in the channel such that the firstportion is electrically isolated from the second portion; placing an LEDin the cavity; electrically connecting the LED between the first andsecond portion of the substrate; and forming a phosphor material overthe LED in the cavity.
 2. The method of claim 1, further comprising:placing an electrostatic dissipation (ESD) chip in the cavity; andelectrically connecting the ESD chip and the substrate.
 3. The method ofclaim 1 wherein the substrate comprises a metal substrate.
 4. The methodof claim 1, further comprising forming a reflective material on aninterior region of the cavity.
 5. The method of claim 4 wherein thereflective material comprises silver or gold.
 6. The method of claim 1wherein forming the cavity comprises forming a blind cavity with abottom surface and a sloped surface surrounding the bottom surface. 7.The method of claim 6 wherein the sloped surface comprises a surfaceinclined at an angle.
 8. The method of claim 6 wherein the slopedsurface comprises a curved surface.
 9. The method of claim 1 wherein thefirst portion comprises a cathodic lead and the second portion comprisesan anodic lead.
 10. The method of claim 1 wherein placing the LED in thecavity comprises placing a plurality of LEDs in the cavity.
 11. Themethod of claim 1 wherein forming the cavity comprises etching thematerial from the substrate.
 12. The method of claim 1 wherein formingthe channel comprises a first etch that removes material from one sideof the substrate to an intermediate depth within the substrate and asecond etch that removes material from an opposite side of the substratein alignment with the first etch.
 13. The method of claim 1, furthercomprising electrically coupling a base portion of the LED to a bottomsurface of the cavity.
 14. The method of claim 13 wherein the bottomsurface is coated with a reflective material, and wherein the baseportion of the LED is electrically coupled to the first portion of thesubstrate through the reflective material.
 15. The method of claim 1wherein the substrate comprises a copper substrate.
 16. A package for alight emitting diode (LED), the package comprising: a first substratesegment having a surface and a depression extending from the surfaceinto the first substrate segment; a second substrate segment spacedapart from the first substrate segment; a spacer between the first andsecond substrate segments, the spacer electrically isolating the firstsubstrate segment from the second substrate segment; an LED in thedepression, the LED having an anodic component and a cathodic component,wherein the anodic component is electrically connected to the secondsubstrate segment and the cathodic component is electrically connectedto the first substrate segment; and a converter material over at least aportion of the LED.
 17. The package of claim 16, further comprising areflective material lining at least a portion of the depression.
 18. Thepackage of claim 17 wherein the reflective material is at least one ofgold or silver.
 19. The package of claim 18 wherein the LED comprises:an N-type GaN material; an InGaN material over the N-type GaN material;and a P-type GaN material over the InGaN material.
 20. The package ofclaim 19 wherein the N-type GaN material comprises the cathodiccomponent, and wherein the LED is surface-mounted to the first substratesegment with the N-type GaN material electrically connected to the firstsubstrate segment.
 21. The package of claim 16 wherein the spacer iselectrically insulative.
 22. The package of claim 19, further comprisinga conductive base layer under the N-type GaN material, wherein the LEDis surface-mounted to the first substrate segment with the conductivebase layer electrically connected to the first substrate segment. 23.The package of claim 16 wherein the first and second substrate segmentsare copper.
 24. The package of claim 16 wherein the spacer comprises afiller molded between the first and second substrate segments.
 25. Thepackage of claim 16 wherein the conversion material comprises a phosphormaterial.
 26. The package of claim 16, further comprising a plurality ofLEDs in the depression.
 27. The package of claim 16, further comprisingan electrostatic dissipation chip in the depression and electricallyconnected to the second substrate segment.
 28. The package of claim 16wherein: at least one of the first or second substrate segment includesat least one of silicon (Si), gallium nitride (GaN), aluminum nitride(AlN), copper (Cu), aluminum (Al), tungsten (W), stainless steel (Fe),and silicon carbide (SiC); the LED includes an N-type gallium nitride(GaN) material, an indium gallium nitride (InGaN) material, and a P-typeGaN material on one another in series; the spacer includes at least oneof a polyimide, a solvent-soluble thermoplastic polyimide, a ceramicmaterial, and glass; and the converter material includes at least one ofcerium(III)-doped yttrium aluminum garnet (“YAG”), neodymium-doped YAG,neodymium-chromium double-doped YAG, erbium-doped YAG, ytterbium-dopedYAG, neodymium-cerium double-doped YAG, holmium-chromium-thuliumtriple-doped YAG, thulium-doped YAG, chromium(IV)-doped YAG,dysprosium-doped YAG, samarium-doped YAG, and terbium-doped YAG.
 29. Apackage for a light emitting diode (LED), the package comprising: afirst substrate portion having a depression on a surface, wherein thefirst substrate portion is metal; a second substrate portion, whereinthe second substrate portion is metal; an electrically insulativematerial between the first and second substrate portions; an LEDpositioned in the depression, wherein the LED has— a first contactsurface-mounted to a base surface of the depression to electricallyconnect the first contact to the first substrate portion; and a secondcontact electrically connected to the second substrate portion; and aconverter material in the depression over at least a portion of the LED.30. The package of claim 29 wherein the second contact is wirebonded tothe second substrate portion.
 31. The package of claim 29 wherein thefirst substrate portion comprises a cathodic lead for the LED and thesecond substrate portion comprises an anodic lead for the LED.
 32. Thepackage of claim 29, further comprising a reflective material lining atleast a portion of the depression.
 33. The package of claim 32 whereinthe reflective material comprises gold, silver, or copper.
 34. Thepackage of claim 29 wherein the first and second substrate portionscomprise copper substrates.